Background: Iron long distance transport in plants is underdocumented. Results: Iron is delivered to embryos as ferric complexes with citrate/malate. An ascorbate-mediated reduction step is further required to acquire iron. Conclusion: Ascorbate plays a key role for the chemical reduction and transport of Fe 2ϩ . Significance: The identification of iron ligands and the transport process is crucial to further understand how iron is distributed within the plant.

The photosynthetic machinery of plants must be regulated to maximize the efficiency of light reactions and CO fixation. Changes in free Ca in the stroma of chloroplasts have been observed at the transition between light and darkness, and also in response to stress stimuli. Such Ca dynamics have been proposed to regulate photosynthetic capacity. However, the molecular mechanisms of Ca fluxes in the chloroplasts have been unknown. By employing a Ca reporter-based approach, we identified two chloroplast-localized Ca transporters in Arabidopsis thaliana, BICAT1 and BICAT2, that determine the amplitude of the darkness-induced Ca signal in the chloroplast stroma. BICAT2 mediated Ca uptake across the chloroplast envelope, and its knockout mutation strongly dampened the dark-induced [Ca ] signal. Conversely, this Ca transient was increased in knockout mutants of BICAT1, which transports Ca into the thylakoid lumen. Knockout mutation of BICAT2 caused severe defects in chloroplast morphology, pigmentation and photosynthetic light reactions, rendering bicat2 mutants barely viable under autotrophic growth conditions, while bicat1 mutants were less affected. These results show that BICAT transporters play a role in chloroplast Ca homeostasis. They are also involved in the regulation of photosynthesis and plant productivity. Further work will be required to reveal whether the effect on photosynthesis is a direct result of their role as Ca transporters.

ObjectivesPlant growth-promoting rhizobacteria (PGPR) may contribute to sustainable crop production by improving plant growth and/or plant tolerance to abiotic stresses. Soil salinity, which limits the productivity of crop plants, is one of the major concerns of modern agriculture, especially in countries heavily affected by climate change as Vietnam. Currently, only a few reports have studied local PGPR isolated in Vietnam, particular Pseudomonas. Therefore, our study aimed to isolate and identify a region-specific Pseudomonas strain and evaluate the effects of this strain on germination, growth promotion and gene expression of Arabidopsis thaliana under salt stress.ResultsThe Pseudomonas named PS01 was isolated from maize rhizosphere collected in Ben Tre province, Vietnam. This strain was identified as a member of the Pseudomonas putida subclade. Pseudomonas PS01 could improve the germination rate of Arabidopsis seeds in 150 mM NaCl. A. thaliana plants inoculated with Pseudomonas PS01 survived under salt stress conditions up to 225 mM NaCl, while all non-inoculated plants were dead above 200 mM NaCl. The transcriptional levels of genes related to stress tolerance showed that only LOX2 was up-regulated, while APX2 and GLYI7 were down-regulated in inoculated plants in comparison to the non-inoculated controls. In turn, RD29A and RD29B did not show any significant changes in their expression profiles.Electronic supplementary materialThe online version of this article (10.1186/s13104-019-4046-1) contains supplementary material, which is available to authorized users.

Calcium (Ca2+) and manganese (Mn2+) are essential elements for plants and have similar ionic radii and binding coordination. They are assigned specific functions within organelles, but share many transport mechanisms to cross organellar membranes. Despite their points of interaction, those elements are usually investigated and reviewed separately. This review takes them out of this isolation. It highlights our current mechanistic understanding and points to open questions of their functions, their transport, and their interplay in the endoplasmic reticulum (ER), vesicular compartments [Golgi apparatus, trans-Golgi Network (TGN), prevacuolar compartment (PVC)], vacuoles, chloroplasts, mitochondria, and peroxisomes. Complex processes demanding these cations, such as Mn2+-dependent glycosylation or systemic Ca2+ signaling, are covered in some detail if they have not been reviewed recently or if recent findings add to current models. The function of Ca2+ as signaling agent released from organelles into the cytosol and within the organelles themselves is a recurrent theme of this review, again keeping the interference by Mn2+ in mind. The involvement of organellar channels [e.g., Glutamate-Receptor-Likes (GLRs), Cyclic-Nucleotide-Gated Channels (CNGCs), Mitochondrial Conductivity Units (MCUs), Two-Pore Channel1 (TPC1)], transporters [e.g., Natural-Resistance-Associated Macrophage Proteins (NRAMPs), Calcium Exchangers (CAXs), Metal-Tolerance Proteins (MTPs), Bivalent-Cation Transporters (BICATs)] and pumps [Autoinhibited Ca2+-ATPases (ACAs), ER Ca2+-ATPases (ECAs)] in the import and export of organellar Ca2+ and Mn2+ is scrutinized, whereby current controversial issues are pointed out. Mechanisms in animals and yeast are taken into account where they may provide a blueprint for processes in plants, in particular with respect to tunable molecular mechanisms of Ca2+-versus-Mn2+ selectivity.